The present invention relates to devices and methods for removing material from within a body, particularly where the volume of material to be removed has at least two dimensions exceeding the lateral dimensions of the opening via which the volume is accessed. In certain preferred embodiments, the invention provides a tool and method for removing material from an intervertebral disc, such as in a discectomy.
Various techniques are known for performing minimal-invasive discectomy. Most commonly, conventional cutting and manipulation tools are used under endoscopic control to sever disc tissue and remove it through a working channel. This approach is slow and tedious, particularly given limitations on the size of incision, and the risk of damage to the dural sac or nerve roots.
US Patent Application Publication No. 2007/0149990 to Palmer et al. proposes a tissue removal apparatus in which an elongated hollow device is formed from shape-memory materials that is biased to a predefined coiled form. The device has lateral cutting openings into which tissue is meant to be drawn under the influence of suction. The device is not sufficiently rigid to define a predictable path, and is described as loosening, tearing or disrupting tissue within the nucleus of the disc during insertion.
The unpredictability of the path that will be followed by the Palmer device during insertion may lead to a risk of perforation and injury. Additionally, the suction-based approach appears impractical for effective removal of material along a long narrow device with openings spaced along its length. Finally, the Palmer tool does not provide any direct volumetric control of the quantity of material removed.
Turning now to PCT Patent Application Publication No. WO 2006/072941 (hereafter “the '941 application”), this teaches a wide range of devices and corresponding applications in which an elongated element is introduced into a body in a straightened configuration and then assumes a curved or coiled configuration within the body. The '941 application is hereby incorporated by reference herein in its entirety. Unless otherwise defined, terminology used herein is used in the same sense as defined in the '941 application.
Certain embodiments described in the '941 application are implemented as hollow elements with an open tip and may perform limited tunneling or other removal of material from within a body. However, they are limited in their capabilities for removal of material from a volume within a body having at least two dimensions exceeding the lateral dimensions of the opening via which the volume is accessed.
Of particular relevance as background to the present invention are the planar spiral implementation of FIGS. 11-12C, and the three-dimensional forms of FIGS. 10, 13 and 14, of the '941 application. As defined there, and as used herein, the term “spiral” is used in its colloquial sense to refer to any shape which spirals inwards/outwards, and is not limited to an exact geometric spiral which is referred to herein as a “perfect spiral”. The spiral formed from a stepped increase in radius of curvature as described here may be preferred due to its simplicity of manufacture. Nevertheless, it will be appreciated that it is possible to vary segment size and/or inter-segment spacing in a continuous manner to achieve a close approximation to a perfect spiral, or any other varying curvature profile desired.
There is therefore a need for a device for insertion into a body via an opening, and for removing material from within the body, which would follow a predefined path and provide controllable volumetric removal of material from a target region within the body.